1. Field of the Invention
The present invention relates to an internal combustion engine control apparatus including a spark plug which is driven by a current interruption-type ignition circuit, for igniting an air-fuel mixture in an internal combustion engine, in particular, a technology of detecting an abnormality in a discharge voltage and a misfire of the spark plug.
2. Description of the Related Art
In recent years, a high compression-ratio technology and a gasoline in-cylinder direct injection technology become more and more important in order to improve fuel efficiency of an internal combustion engine (gasoline engine). When a compression ratio is increased, however, a pressure in a spark discharge gap in a spark plug is increased to disadvantageously increase a discharge voltage of the spark plug. Moreover, when the gasoline in-cylinder direct injection is performed, a difference in density is likely to be generated in an air-fuel mixture. Thus, large spark energy is required to ignite the air-fuel mixture.
When the spark energy increases, electrodes of the spark plug are likely to wear. As a result, if the electrodes wear, the spark discharge gap becomes wider to increase the discharge voltage of the spark plug. Accordingly, there is a fear in that the discharge voltage of the spark plug exceeds a dielectric withstand voltage to cause dielectric breakdown of the spark plug. Moreover, when the discharge voltage of the spark plug exceeds a magnetically induced voltage which can be generated by an ignition coil, the spark plug cannot generate the spark discharge and therefore cannot ignite the air-fuel mixture.
As a related-art internal combustion engine control apparatus which solves the problem described above, there exits one configured to measure the discharge voltage of the spark plug to obtain a degradation state of the spark plug (for example, see Japanese Patent Application Laid-open No. 2013-177881).
However, the related art has the following problems.
According to Japanese Patent Application Laid-open No. 2013-177881, although a state in which the discharge voltage of the spark plug becomes high can be obtained, a state in which the discharge voltage becomes abnormally low or the occurrence of a spark plug misfire cannot be obtained. Moreover, in order to detect the abnormality in the discharge voltage and the misfire of the spark plug, special elements such as a zener diode which withstands a high voltage are required. Further, an additional wiring for connecting the above-mentioned elements to a secondary coil at a high voltage and insulating processing are required. Thus, costs disadvantageously increase.